Permanent Impairment Rating Calculator
Calculate Combined Values using the standard medical impairment formula.
Combined Whole Person Impairment:
Understanding Impairment Rate Calculation
In medical-legal contexts, specifically within workers' compensation and personal injury law, an impairment rating represents the permanent loss of function to a body part or system. When a person suffers multiple injuries, the ratings are not simply added together (e.g., 10% + 10% does not equal 20%). Instead, they are combined using a specific formula to ensure the total impairment never exceeds 100% of the person.
The Combined Values Formula
Most jurisdictions use the AMA (American Medical Association) Guides to the Evaluation of Permanent Impairment. The formula used is:
Where 'A' is the larger impairment and 'B' is the smaller impairment. This method accounts for the "diminishing returns" of multiple injuries. The first injury reduces the "whole person" from 100% to 80%, so the second injury is only a percentage of the remaining 80%.
If a worker has a 20% impairment of the spine and a 10% impairment of the knee:
1. Start with the largest: 20% (0.20).
2. Take the second: 10% (0.10).
3. Calculation: 20 + 10(1 – 0.20) = 20 + 10(0.80) = 20 + 8 = 28% Whole Person Impairment.
Why Addition Isn't Used
Simple addition is avoided because it would be mathematically possible for a person to be more than 100% impaired, which is logically impossible in medical evaluations. By using the combined values chart or formula, each subsequent impairment is applied to what "remains" of the person's functionality.
Common Use Cases
- Workers' Compensation: Determining Permanent Partial Disability (PPD) settlements.
- Veterans Affairs (VA): Calculating disability compensation for multiple service-connected conditions.
- Personal Injury Litigation: Quantifying long-term damages after an accident.